104 THE PHYSIOLOGY OF INSECT SENSES 



comprising the whorls on the antennae of male Culex vibrated in the 

 presence of a vibrating tuning fork he did not indeed prove, as many 

 authors have pointed out (e.g., Fulton, 1928), that the antennae are 

 auditory organs. Nor did his experiments impHcate the Johnston's 

 organ. Furthermore, since the different forks employed gave different 

 intensities, and hence stimulus energy could not be controlled, the fact 

 that the hairs vibrated most extensively at 512 c/s is not especially 

 significant. In an experiment with Culex pipiens pallens in which 

 intensity was controlled, Yagi and Taguti (1941) found that the hairs 

 which vibrated in the stimulus frequency range of 193-870 c/s vibrated 

 most widely at 217 c/s. As Mayer had shown, maximum vibration 

 occurs when the sound wave advances at right angles to the longi- 

 tudinal axis of the hairs. 



The literature is replete with accounts of mosquitoes reacting to 

 sound. In a most extensive study Roth (1948) found that males of 

 Aedes aegypti respond to the sound of a flying female and to artificial 

 sounds of comparable frequencies by orienting to the source of sound 

 and displaying the mating response, which consists of seizing and 

 clasping. To sounds of other frequencies they: rub the antennae with 

 the forelegs, rub the hind legs together, rub the abdomen or wings with 

 the hind legs, jerk the body, suddenly fly, or suddenly become 

 immobile. 



The frequencies which induce the mating response are different 

 for males of different ages. The effective range extends from about 

 100 to about 800 c/s, and the spectrum is narrower for non- virgin 

 males. For virgin and non-virgin alike the effective band widens with 

 age. This shift to higher frequencies has been correlated with the ex- 

 tension of the antennal fibrillae. When males first emerge, the hairs or 

 fibrillae He recumbent along the shaft of the flagellum. By 48 hours 

 they are fully extended. This correlation suggests either that the apical 

 fibrillae vibrate at higher stimulus frequencies than the lower or that 

 a larger total of fibrillae must be set in motion at higher stimulus 

 frequencies in order to mediate a response. 



Males can be adapted to one frequency (as judged behaviourally) 

 and still retain responsiveness to other frequencies (Roth, 1948). Since 

 intensities were not controlled in these experiments, the significance is 

 in doubt. With minor deviations the same story holds for Anopheles 

 quadrimaculatus, Culex pipiens, and Psorophora confinnis. 



The correlation between the degree of extension of antennal fibrillae 

 and the extension of responses to higher stimulus frequency suggests 

 that the fibrillae are concerned with sound reception ; however, they 



